The present invention relates to an improved biasing arrangement for holding adjacent heat absorbent element sheets of a rotary regenerative heat exchanger in a continuously tight relationship.
In rotary regenerative heat exchange apparatus a mass of tightly packed heat absorbent element sheets is contained in a rotor that is slowly rotated about its axis. The rotor is comprised of a cylindrical rotor shell and divided into sector shaped compartments that house element baskets that contain sheets of heat absorbent material. A basket of heat absorbent material is first positioned in a gas passageway to absorb heat from gases passing therethrough, and then as the element becomes heated it is slowly rotated into a second passageway where it gives up its heat to cooler air passing therethrough. Movement of the rotor is usually continuous so there is a uniform transfer of heat from the hot gas to the cooler air. Some or all of the element sheets are usually formed with corrugations or other formations that extend between inlet and outlet ends of the rotor to direct gas and air flow therethrough and to act as stiffeners for the individual sheets.
The gas passing through the heat exchanger is not only hot but very corrosive, but also has particles of flyash therein, thus the element quickly corrodes and erodes from the effects of the gas. As the sheets of element corrode, and erode, thus becoming thinner and more brittle, they become loose and begin to vibrate until they break up and cause a complete loss of effectiveness.
This vibration is caused particularly by a blast of high pressure air or steam being blown through the spacing between element sheets to remove deposits such as soot and flyash therefrom. Additional vibration of the heat exchange plates is caused by continuous rotation of the rotor. This is especially true when the rotor is being moved about a horizontal axis. Thus, as the rotor is turned about its axis, the plates loosened by corrosion and erosion are further agitated and break apart. Attempts have been made to correct this untenable condition by arrangements shown in U.S. Pat. No. 3,379,240 of Bellows and Woolard, and U.S. Pat. No. 3,314,472 of Krumm and Casagrande.
In U.S. Pat. No. 3,379,240 an arcuate pressure plate with a single arcuate ridge is arranged with the ridge parallel to the flow of gas and air through the rotor. This pressure plate exerts a force along it's opposite surfaces parallel to to the corrugations or other formations on the element sheets. U.S. Pat. No. 3,314,472 discloses an arcuate spring plate with a single arcuate ridge exerting a force against the center of each basket which also lies parallel to the flow of fluid through the heat exchanger and generally parrallel to the corrugations of the element sheets.
While both arrangements defined by the foregoing patents are partially effective, they fail to exert a constant, even force on widely spaced portions of the element sheets for long periods of operation. Moreover the arcuate spring plate tend to exert a concentrated force along a single line that bends the element and causes premature breakage. Furthermore, line of contact between the spring plate and the adjacent element extends parallel to the line of fluid flow through the heat exchanger and thereby lies substantialy parallel to the corrugations shown on the adjacent element sheets. Therefore, portions of each element sheet that lie remote from contact with the spring plate tend to vibrate and quickly deteriorate until they are ultimately destroyed.